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EXAMINATION OF INSOLUBLE SUBSTANCES.
The following substances are, under certain circumstances, insoluble in acids, and must be examined specially :-Silica, Silicates, Aluminia, Aluminates, Oxides of Antimony, Chromium, and Tin, Chrome Iron Ore, Sulphates of Barium, Strontium, and Lead, certain Fluorides (e.g. of Calcium), certain Sulphides (e.g. of Lead), the Chloride, Bromide, and Iodide of Silver, Carbon, and Sulphur.
Heat the substance in a dry tube, and observe whether(a) It fuses and volatilizes completely. Sulphur (smells of S02). 16) It fuses, but does not volatilize. Chloride, Bromide, or
Iodide of Silver. (Yields metallic silver on fusing on
charcoal with Na, CO3). (c) It is infusible, but disappears on heating. Carbon (Deflagrates
when heated with K NO3). (d) It is infusible, but darkened in colour while hot, regaining its colour
on cooling. Tin Dioxide and Antimony Pentoxide. (Confirm by blow-pipe test-tin bead is malleable ; antimony bead
brittle.) Observe whether(e) It yields a green bead with borax or microcosmic salt. Chromium
Oxide or Chrome Iron Ore.
Silicates. (Fuse with four times its weight of a mixture of
gelatinous mass.) (8) It yields a colourless bead, with microcosmic salt. Alumina.
(Heated on charcoal and moistened with Co (NO3)2 and re-heated,
it yields a blue infusible mass.) (h) It is white and infusible, but quite unaltered by heating.
Lead Sulphate yields, when heated with Na, CO3 in blow-pipe
reducing flame, malleable metallic bead. (See also :-)
Barium Sulphate, fused with Na2CO3 and HCl added, yields
Ba Cl2 (flame coloration, green), precipitated by Sr SO4 solution. Strontium Sulphate, fused with Na, CO3 and HCl added,
yields Sr Cl2 (flame coloration, crimson), precipitated by Ca SO4
solution. Calcium Fluoride, heated with H, SO4, yields H F, which
etches glass. (i) It is black and infusible, and yields a malleable metallic bead when
fused with Na, CO3 in the blow-pipe flame. Lead Sulphide. (Bead leaves black mark on paper; and, when dissolved in H NO3, gives a white precipitate on addition of H, SO4.)
REACTIONS OF THE COMMONLY OCCUR.
RING METALS, WITH THE METHODS
GROUPING OF THE METALS.
62. The metals are divided into five groups according to their behaviour with certain substances which are termed group reagents. These five groups are the following
GROUP 1.-(SILVER GROUP.)*
Group reagent, HCI.
Silver, Mercury, Lead.
The chlorides of the metals of this group are insoluble in water, and are therefore precipitated on addition of HCI.
* A characteristic metal in each group may conveniently be used to designate that group. Thus, we may say, Silver Group” and “Copper Group,” in place of Groups 1. and D.
GROUP II. (COPPER GROUP.)
Group reagent, H2S in presence of HCI.
Mercury, Lead, Bismuth, Copper, Cadmium, Arsenic,
Antimony, and Tin.
The sulphides of the metals of this group are insoluble in HCl, and are therefore precipitated by H S in an aqueous solution containing HCl. The three last metals, arsenic, antimony, and tin, form a subgroup, as their sulphides are soluble in (NH4)2S,, whilst the sulphides of the remaining metals are insoluble in that reagent.
GROUP III. (IRON GROUP.)
Group reagent, (NH4),S, in presence of NH4Cl and
Iron, Nickel, Cobalt, Zinc, Aluminium, Manganese,
The sulphides and hydrated oxides of the metals of this group are insoluble in water, and are therefore precipitated on addition of the group reagent. Aluminium and chromium are precipitated as hydrated oxides, the others as sulphides,
GROUP IV. (BARIUM GROUP). Group reagent, (NH4)2CO3, in presence of (NH)HO
Barium, Strontium, Calcium:
The carbonates of the metals of this group are insoluble in water, and are precipitated on the addition of (NH4)2CO3; as, however, they are soluble in acids, (NH2)HO must be added when the solution is acid.
GROUP V. (POTASSIUM GROUP.)
Metals unprecipitated by the above group reagents.
Magnesium, Potassium, Sodium, Ammonium.
These metals have no common precipitant, and are therefore distinguished by individual tests.
The student should at first have several metallic salts given to him, and be asked merely to determine to which of the above groups each salt belongs ; he ought next to make himself familiar with the individual tests for each metal which follow, and then proceed to the separations of the different metals. It will also be well for him to attempt to frame a table of separations for each group before consulting those given in the book.